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A Description of Plastic Injection Molding

The products made in plastic injection molding start out as basic plastic pellets. These pellets are then fed in to a huge machine whose tonnage is around twenty five. This huge device then melts the plastic into a molten state and forces it into a molding using an injector.

This mold may be an infinite number of sizes and shapes. In simple terms, plastic injection molding is just molten plastic forced into a molding until it cools and hardens into the final product. Plastic Injection Molding is used when a product design is to complicated or it is to expensive to make the part by machining, and is very useful when producing bulk products, since the same mold can be used over and over again.
The entire procedure of plastic injection molding consists of the following 6 phases:

1) CLAMPING - The 3 components of the molding machines are the injection units, the molds, and the clamps. The clamps function is to keep the mold pressurized at a constant level so that the molten plastic coats it's surfaces uniformly.

2) INJECTING - The injection process startsstarts by loading the plastic pellets in to the "hopper" located on top of the injecting unit which leads in to the cylinder. The pellets are then brought up to the temperature where they become molten and then this material is stirred by a mixer until it is the correct consistency. A screw or "ram" then forces this material into a mold by way of a sprue.

3) DWELLING - Dwelling is where the mold is then pressurized to a level where the molten plastic will be forced into all parts and little crevices in the mold. If this procedure is done incorrectly and the mold isn't coated properly, it will result in the part being scrapped.

4) COOLING - Cooling must be done carefully and slowly, because if the cooling process is too quick, it can result in the product being warped or sticking to the walls of the mold.

5) OPENING the MOLD - After cooling, the two halves of the mold are released by the clamp unit and separated. This is a careful process, because the molds can be very costly, and are vital in that they are reused continuously throughout the products life.

6) EJECTING - The last part of the process is ejecting the final product from the mold with ejection pins. The part is then either ready for inspection and packaging, or it is conveyed on to the next stage of the manufacturing process.

Although plastic injection molding is responsible for many of the products that we use everyday, and because of it's use in the automotive industry, cars are much more affordable these days, it does have it's drawbacks. The equipment needed to run a plastic injection molding company is large, complex, and requires a large amount of money on the front end. The process it self is also not very economical if the product you have designed does not need to be mass produced.

That being said, the advantages of plastic injection molding such as, reduced labor fees, low wastage of materials, quick production times, and no finishing steps far outweigh these draw backs making plastic injection molding one of the most efficient manufacturing forms available.


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Plastic Part Design For Injection Molding
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